Geochemical exploration method



April 17, 1956 E. E. BRAY 2,742,575

GEOCHEMICAL EXPLORATION METHOD Filed July 14, 1952 3 Sheets-Sheet l TRA NSM/SS/ON WAVE LENGTH /2 /3 /4 ELLIS E, EBAY WAVE LENGTH INVENTOR.

ATTUHNEY April 17, 1956 Filed Jul 14, 1952 TPANSM/SS/ON "/0 TRANSMISS/ON TRANSM/SS/ON WA VE LENG TH E. E. BRAY GEUCHEMICAL EXPLORATION METHOD 3 Sheets-Sheet 2 WA v5 L ENG TH WA I/E LENG TH ELLIS E ERAY I N VEN TOR.

B MW 809M A T TUHNE Y April 17, 1956 E. E. BRAY 2,742,575

GEOCHEMICAL EXPLORATION METHOD Filed July 14, 1952 3 Sheets-Sheet 3 ELLIS E, EBAY INVENTOR.

BY vi aw A T TUHNE Y United States Patent 2,742,575 GEOCHEMICAL EXPLORATION METHOD Ellis E. Bray, Dallas, Tex., assignor, by mesne assignments, to Socony Mobil Oil Company, Inc., a corporation of New York 1 Application July 14, 1952, Serial No. 298,796

12 Claims. 01. 250-43.s

This invention relates to geochemical exploration and relates more particularly to geochemical exploration for subterranean petroleum reservoirs.

In the location of subterranean petroleum reservoirs, use has been made of geochemical methods. These methods are based on the theory that hydrocarbons migrate upwardly from the subterranean reservoir and the presence, in the surface or near surface zones of the earth or in the earth strata intermediate to the surface or near surface zones of the earth, of hydrocarbons or organic derivatives thereof is indicative of the presence of a subterranean petroleum reservoir. Thus, as a prospecting method or a well logging method, samples of earth material have been collected and analyzed for hydrocarbons or organic derivatives thereof and the concentrations of hydrocarbons or organic derivativesthereof have been correlated with the locations from which the samples were taken to obtain information as to the probable location of the petroleum reservoir.

It has been recognized that hydrocarbons may be pres ent in the earth as the result of conditions other than migration from a subterranean petroleum reservoir. For example, it is recognized that methane, a hydrocarbon constituent of petroleum can be present in the earth as a result of vegetative decomposition and that heavier hydrocarbons, which could be constituents of petroleum, can be present in the earth as a result of bacterial action. Thus, a geochemical prospecting method, to be positive with respect to the probable location of, a subterranean petroleum reservoir, should be'capable of identifying hydrocarbons or organic derivatives thereof in earth samples as having their origin in a subterranean petroleum reservoir. It would appear then that it would be a simple matter to obtain a positive indication of the presence of a subterranean petroleum reservoir by merely analyzing earth samples for hydrocarbons or'organic derivatives thereof that could be present in the earth samples only because of migration of hydrocarbons from a subterranean petroleum reservoir. However, the quantity of hydrocarbons or organic derivatives thereof present in earth samples, even when taken from localities overlying a subterranean petroleum reservoir, is so small as tomake it diflicult to identify even the simple hydrocarbons therein much less to identifythe morecomplex hydrocarbons or their organic derivatives. But of greater difiiculty is the fact that, in so far as I am aware, no means have been heretofore known tov ascertain whether any hydrocarbons or organic derivatives thereof in earth samples have had their origin in a subterranean petroleum reservoir. r g

It is an object of this invention to provide a geochemical exploration method for the location of subterranean petroleum deposits. It is another object of this invention to provide a method for analyzing earth samples. It is another object of this invention to provide a method for identifying earth sample constituents as having an origin in petroleum. These and further objects of the in- 2,742,575 v Patented Apr. 17, 1956 ICC samples, and infrared radiation is passed through each of the extracts over a range of Wave lengths which specifically includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns to obtain a transmittance curve of each of the extracts or to determine otherwise absorptionof the infrared radiation by the extracts over the range of wave lengths employed. 1

Figure 1 is an infrared radiation transmittance curve of a solution of weathered crude petroleum.

Figure 2 is an infrared radiation [transmittance curve of an extract of an earth sample taken in an area located overan oil seep.

Figure 3 is an infrared radiation transmittance curve of an extract of an earth sample contaminated with crude petroleum oil.

Figure 4 is an infrared radiation transmittance curve of an extract of an earth sample taken from an area not related to any known subterranean petroleum reservo1r.

Figure 5 is an infrared radiation transmittance curve of an extract of an earth sample taken from another area not related toany known subterranean petroleum reservoir.

Figure 6 is a map showin'g sampling points taken on a V traverse over a known oil field, I

microns. Stated otherwise, I have discovered that curves of transmittance versus wave length for infrared radiation through crude petroleum oil will always exhibit ab sorption bands at 12.35:.10 microns and 13.40:;10 microns. Further, I have discovered, through extensive research, that the property ofcrude petroleum oil of selectively. absorbing infrared radiation having wave lengths of 12.35310 microns and 13.401110 microns is not destroyed after removal of the crude petroleum oil from its subterranean reservoir and retention. forextremely long periods of. time in other earth material where it is subject to such diverse conditions as oxidation, bacteria} action, weathering, or other conditions depending upon the location and environment of the earth material. Additionally, I have discovered that earth samples. taken from-localities in proximity to a subterranean pteroleum reservoir will contain constituents capable of selectively absorbing infrared radiation having wave lengths of 12.351110 microns and 13.40:.10 microns whereas earth samples taken from localities where there is no possibility of the proximity of a subterranean petroleum reservoir will not contain constituents capable of selectively absorbing infrared radiation having these wave lengths. Thus,fthe detection inearth samples of a constituent or constituents capable of selectively absorbing infrared radiation having wave lengths, of 12.351110 microns and 13.40:.10 microns identifiesthe constituent of selectively absorbing infrared radiation having wave lengths of 12.35:.10 microns and 13.40:.10 microns.

For example, the paraflin constituents-of crude petroleum oil or their organic derivatives do not exhibit this property. However, while the property of selectively absorbing infrared radiation having the wave lengths of 12.35:.10 microns and 13.40:.10 microns is not shared by all constituents, or their organic derivatives, of crude petroleum oil, crude petroleum oil contains a constituent or constituents exhibiting this property and the constituent or constituents exhibiting this property migrate through the soil from a subterranean petroleum reservoir as postulated for any constituent of the crude petroleum oil.

In the practice of the invention, earth samples are collected from the prospect area. Where exploration is con ducted by prospecting over a surface area of the earth, the samples are preferably collected from points set out in the area according to a definite plan or pattern. For example, the sampling points may be spaced at regular intervals, say about of a mile along a traverse, or along a series of traverses, or along a grid pattern. However, any suitable interval spacing may be employed. Sampling over a surface area is generally conducted by taking the earth samples either from the surface zones .or

the near surface zones. Preferably, the samples are taken at a distance of at least one foot from the surface in order to avoid as much as possible any contamination or excessive content of'organic debris. Where exploration is conducted in connection with the drilling of a well, the earth samples, comprising cores or cuttings, may be obtained from successive depths in the well as desired. Generally, sampling may be carried out whether over the surface of the earth or from successive depths in a'well in accordance with any of the patterns and any of the procedures heretofore employed in the art.

After collection, the earth samples are dried and crushed and a portion of each, which may be of the order of 150 grams, is extracted with a suitable solvent. Any solvent capable of desorbing and dissolving hydrocarbons from the earth samples may be employed for extraction. Suitable solvents include carbon tetrachloride, chloroform, carbon disulfide, acetone, methanol, ethanol, propanol, diethyl ether, benzene, etc. Mixtures of solvents may also be employed, such as an equimolar mixture of an alcohol and carbon tetrachloride or a mixture comprising about ten volumes of benzene and one volume of methanol. The extraction of the soil samples may be carried out in any know manner, as, for example, by employing a Soxhlet extractor or a ball mill extractor.

The solutions of extract thus obtained may be filtered, if required, and without further treatment, subjected to analysis by passing the infrared radiation therethrough and obtaining the transmittance curve or otherwise measuring the absorption of the infrared radiation, assuming that the solvent in which the extract is dissolved does not absorb the infrared radiation so as to mask any absorption bands over the range of wave lengths measured. Preferably, however, the solutions of extract are Weathered in order to obtain extracts which are uniform with respect to the removal therefrom of any volatile constituents extracted from the earth samples. Weathering may be accomplished by filtering, if required, or, in lieu of filtering, decanting from any earth sample residue, heating to a temperature sufficiently high to vaporize the solvent and any volatile constituents of the earth sample, and blowing a stream of air or other suitable gas thereover during the heating period. A suitable temperature for weathering is 40 C., and weathering is continued at the temperature employed until the extract comes to constant weight. The extract, after removal of the solvent, is in the form of a waxy semi-solid.

Following weathering, the extract per se may be subjected to transmission of infrared radiation or the extract may be dissolved in a suitable solvent and the infrared radiation transmitted through the solution of extract. For transmission and measurement of the infrared radiation, any suitable spectrophotometer apparatus capable of measuring intensity of infrared radiation as a function of wave length over the'desired range of wave lengths may be 4 employed. A suitable spectrophotometer apparatus comprises an infrared radiation source, such as a globar, or a Nernst lamp, a plate or other holder for the extract per se or an absorption cell for the solution of extract, and a spectrometer having a thermocouple and a galvanometer or amplifier operatively connected therewith.

The absorption of infrared radiation by the extract per so may be carried out by coating the extract or a portion thereof on a plate, such as a rock salt plate, transparent to the infrared radiation over the range of wave lengths employed, and passing the infrared radiation therethrough. It is preferred, however, to dissolve the extract in a suitable solvent transparent to the radiation over the wave lengths employed to obtain a solution of the extract, placing the extract solution or a portion thereof thus obtained in the absorption cell of the spectrophotometer and passing the infrared radiation therethrough. A suitable solvent is carbon disulfide.

The infrared radiation passed through the extract of each earth sample must have a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns. It is the presence of absorption bands at these wave lengths that characterizes the earth sample extract as containing hydrocarbons or-organic derivatives thereof having their origin in crude petroleum oil and in order to recognize the presence of these hands, it is necessary to measure the absorption of the infrared radiation at wave lengths somewhat below and somewhat above 12.35:.10 microns and somewhat below and somewhat above l3.40:.10 microns. Generally, I prefer to measure the absorption of the infrared radiation over the range between 12 and 14 microns to obtain a continuous record or scanning of the spectrum between these wave lengths.

To measure the absorption of the infrared radiation by the extract, the infrared radiation from the source is passed through the extract and the spectrophotometer is operated in conventional manner to determine the trans mittance of the infrared radiation passing through the extract, i. e., to determine the per cent of the incident radiation transmitted through the extract, over the range of wave lengths employed. Where the extract contains hydrocarbons or organic derivatives thereof having their origin in crude petroleum oil, the transmittance of the radiation is lower at the wave lengths of 12.35:.10 microns and 13,401.10 microns than it is at adjacent wave lengths and two absorption bands will be present in the spectrum of the transmitted radiation. It is only necessary to determine the presence or absence of the absorption bands at 12.35:.10 microns and 13.40:.10 microns to determine the presence or absence in the extract of constituents having their origin in petroleum.

it'is often desirable, as, for example, where a series of extracts exhibit these absorption bands, to determine relatively the amount of petroleum hydrocarbons or organic derivatives thereof in each of the earth samples. This may be determined in conventional manner, if the absorption bands are exhibited to a sufficiently prominent extent, from knowledge of the weight of the earth sample, the portion of the extract therefrom employed in measuring the absorption of the infrared radiation, the intensity of the infrared radiation prior to passage through the extract, i. e., the incident radiation, the amount of the infrared radiation absorbed by the plate holding the extract or absorbed by the absorption cell and the solvent where a solution of extract is employed, and application of Beers law that the concentration of the material absorbing radiation is a function of the cologarithm of the per cent transmission.

Occasionally, earth samples may be found which contain hydrocarbons or organic derivatives thereof having their origin in crude petroleum oil but which may contain such a quantity of organic debris or other materials relative to the hydrocarbons or organic derivatives therecoated on roads.

of having their origin in crude petroleum oil that 'the absorption bands of the infrared radiation at the wave lengths of 12.35:.10 microns and 13.40:.10 microns become masked. In such cases, the organic debris and other materials may be separated to a satisfactory extent from the hydrocarbons-or organic derivatives thereof in the extract by employing adsorption-fractionation. Absorption-fractionation is a well known technique and any of the procedures known to the art may be employed for treatment of the extract.

Hydrocarbons or organic derivatives thereof having their origin in crude petroleum oil but not due to migration from a subterranean petroleum reservoir'may occasionally be found in earth samples. Hydrocarbons or organic derivatives thereof having their origin in crude petroleum oil may be present, for example, in earth samples as a result of contamination by petroleum oil leaking from a pipe line or by petroleum oil which has been Contamination from sources such as these is readily recognizable and the presence ofpetroleum hydrocarbons or organic derivatives thereof in earth samples from these sources will he obviously regarded as having no significance with respect to the location of a subterranean petroleum reservoir. Further, hydrocarbons or organic derivatives thereof having their origin in crude petroleum oil may sometimes be detected by the present invention in ancient shales.

in ancient shales is not significant with respect to'the location of a subterranean petroleum reservoir inasmuch as ancient shales are believed to be a source bed of petroleum hydrocarbons and the hydrocarbons are in quantity insufiicient to create a reservoir or could not migrate therefrom to structure favorable for a reservoir. Ancient shales are readily recognized by geologic considerations and the detection in ancient shales of hydrocarbons or organic constituents thereof having their origin in crude petroleum oil will also be obviously regarded as having no significance with respect to the location of a subterranean petroleum reservoir.

The following examples will be illustrative of the invention.

EXAMPLE 1 A sample of crude petroleum oil was weathered at 40 C. with an air jet until the sample had attained constant weight. A portion of the weathered sample residue weighing 200 milligrams was dissolved in one cubic centimeter of carbon disulfide and a portion of the resulting solution was placed, in the absorption cell of an infrared spectrophotometer. Infrared radiation between the wave lengths of 12 and 14 microns was passed through the absorption cell and the transmittance over these wave lengths was measured. Figure 1 is a graph of the transmittance of the radiation over the wave lengths between 12 and 14 microns. In the figure, as well as in all the other figures, the abscissa is the wave length of the radiation in microns and the ordinate is the transmittance as expressed as per cent transmission of the incident radiation. It will be observed from inspection of the figure that strong absorption bands occurred at 12.30 microns and between 13.40 and 13.45 microns. A strong absorption band appeared at 13.90 microns, but this band is not unique with respect to crude petroleum oil and is However, the pres-' ence of these hydrocarbons or organic derivatives thereof air jet to constant weight. The weathered extract was then dissolved in one cubic centimeter of carbon disulfide,

' a one-half cubic centimeter portion thereof was placed 13.35 and 13.45 microns indicating the presence in the earth sample of constituents having their origin in crude petroleum'oil. It will also be observed that the absorption band at 13.90 microns appearing in Figure 1 is absent from Figure 2.

EXAMPLE 3 An earth samplev was taken from the surface zone in an area that was known to have been contaminated intermittently over a period of twenty years by leakage of crude petroleum oil from a nearby well. The sample was treated and the absorption of I infrared radiation measure in the same manner as described above in Example 2. Figure 3 is a graph of the intensity of the transmitted radiation. It will be observed from Figure 3 that the extract exhibited two absorption bands, one between 12.35 and 12.40 microns and the other between exhibited by various types of organic materials includ- I ing organic debris in earth samples. EXAMPLE 2 A soil sample was taken from the surface zone of the earth in an area located over an oil seep. A portion of the earth sample weighing 150 grams was dried and crushed and extracted with 175' cubic centimeters of a solvent consisting of 10 volumes of benzene and one volume of methanol. The solvent containing the extract dissolved therein was filtered from the earth sample and the filtered solution was weathered at 40 C. with an 13.35 and 13.45 microns, indicating the presence in the earth sample of constituents having their origin in crude petroleum oil. It will also be observed that the extract exhibited the absorption band at 13.90 microns as did the extract in Example 1. 7

As shown in Examples 1, 2 and 3, petroleum crude oil, an extract of an earth sample taken from an area located near an oil seep, and an extract of an earth sample taken from an area previously contaminated by crude petroleum oil, respectively, exhibited strong absorption bands in the wave lengths of 12.35:.10 and13.40:.l0 microns. Examples 4 and 5 following, exhibit the fact that all earth samples will not exhibit these absorption bands.

' j EXAMPLE 4 j the extract determined in the same manner as described above for the samples in Examples 2 and 3. Figure 4 is a chart of the transmittance versus wave length of the infrared radiation. As shown by the figure, the only ab-' sorption band exhibited by the sample between the wave lengths of 12 and 14 microns is the band at 13.90 microns. The presence in the earth sample of constituents having their origin in crude petroleum oil is therefore not indicated.

EXAMPLE 5 earth sample of any constituents having their originin crude petroleum oil was not indicated.

XAMPLE 6 A number of earth samples were taken from the surface of the earth in the Wills Point formation in Texas on a transverse extending across a known subterranean petroleum reservoir. Each sample weighing grams was dried and crushed and extracted by ball milling the dried and crushed sample in the presence of 150 cubic centi- 7 meters. of a solvent consisting of 10-volun1es of benzene and one volume of methanol. The solvent was. filtered from: each sample, weathered at 40 C. with an air jet,

and each of the resulting weathered extracts was dissolved in one-half cubic centimeter of carbon disulfide. A .3 cubic centimeter portion. of each of the carbon disulfide solutions of the extracts was placed in the absorption cell of an infrared spectrophotometer, and a transmittance curve of infrared radiation between the wave lengths of 12 and 14 microns was obtained for each of the solutions of extract.

Figure 6 is a map of the sampling area showing the locations of the sampling points and of the subterranean petroleum reservoir. Referring to the figure, samples were taken from sampling points 10, 11:, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Sample points 10 to 18 were about one mile part and were on a traverse extending between the line 21 indicating the top line of the Wills Point formation at the surface of the earth and line 22 indicating the bottom line of the formation at the surface of the earth the traverse passing over the subterranean petroleum reservoir 23. Samples were taken from points 19 and 20 as a check on the samples taken from points 12 and 13.

The following table gives the sampling point number and notation as to whether the extract of the earth sample taken from the sample point exhibited absorption bands in the infrared transmittance curve at 12.35:.10 microns and 13.40:.10 microns, the word positive indicating that bands were exhibited and the word negative indicating that such bands were not exhibited.

Table 1 Sample point No.: Exhibition of absorption bands 10 Negative 11 Negative 12 Positive 13 Positive 14 Positive 15 Negative 16 Negative 17 Negative l8 Negative l9 Positive 20 Positive It will be seen from the table that the extracts of samples taken from sampling points 12, 13, 19, and 20 directly over the subterranean petroleum reservoir 23 exhibited infrared radiation absorption bands at 12.35: .10 microns and 13.40:.10 microns, indicating the presence in the sample of constituents having their origin in crude petroleum oil. It will also be seen from the table that extracts of samples taken from sampling points 10, 11, 16, 17, and 18 located away from the subterranean petroleum reservoir 23 did not exhibit absorption bands at 12.35:.10 microns and 13.40:.10 microns, indicating the absence from the sample of constituents having their origin in crude petroleum oil. The extract of samples from sampling point 14 also shows the absorption bands at 12351.10 microns and 13.40-11.10 microns indicating the migration of constituents of crude petroleum oil from the reservoir 23 upwardly and to one side of the reservoir.

Herein, and in the appended claims, by oxtract" I mean that portion of the earth sample which has been re moved from the earth sample by extraction with a solvent and which may or may not be in solution in a solvent. By solution of extract, I mean the extract in solution in a solvent.

Having thus described my invention it will be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

I claim:

1. The method of geochemical exploration for a sub.- terranean petroleum reservoir comprising collecting earth samples from an exploration zone, obtaining an extract from each of said earth, samples containing any hydrocarbons and organicderivatives thereof which may have been present; in said earth samples, transmitting through each of said extracts infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.35:.10 microns and over a range of wave lengths which includes at least the wave length of 13.40:.10 microns transmitted through each of said extracts.

2. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of desorbing and dissolving any hydrocarbons and organic derivatives thereof contained in said earth samples to obtain an extract from each of said, samples, transmitting through each of said extracts infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.35:.10 microns and over a range of wave lengths which includes at least the wave length of 13.40:.10 microns transmitted through each of said extracts.

3. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of desorbing and dissolving any hydrocarbons and organic derivatives thereof contained in said earth samples to obtain an extract from each of said samples, transmitting through each of said extracts infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns, each of said extracts being dissolved in a solvent which will not absorb said infrared radiation, and determing the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.35 :.10 microns and over a range of wave lengths which includes at least the wave length of 13.40:.10 microns transmitted through each of said extracts.

4. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of dcsorbing and dissolving any hydrocarbons and organic derivatives thereof contained in said earth samples to obtain a solution of extract from each of said samples, removing said solvent from each of said solutions of extract, transmitting through each of said extracts infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.35:.10 microns and over a range of wave lengths which includes at least the wave length of 13.401210 microns transmitted through each of said extracts.

5. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of desorbing and dissolving any hydrocarbons and organic derivatives thereof contained in said earth samples to obtain a solution of extract from each of said samples, weathering each of said solutions of extract to remove solvent and any readily volatile constituents therefrom, dissolving each of said weathered extracts in a solvent which will not absorb infrared radiation, transmitting through each of said extracts infrared radiation having a range of wave lengths which includes the wave lengths of 12.35: ;.10 microns and 13.40:.10 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths'which' includes at least the wave length of 12351.10 microns and over a range of wave lengths which includes at least the wave length of 13.40:.10 microns transmitted through each of said extracts.

6. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of desorbing and dissolving any hydrocarbons and organic derivatives theresaid solutions of extract at the same temperature to remove solvent and any readily volatile constituents therefrom, dissolving each of said weathered extracts in carbon disulfide, transmitting through each of the resulting solutions of said extracts infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.351210 microns and over a range of wave lengths which includes at least the wave length of 13.40:.10 microns transmitted through each of said extracts. V

7. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, obtaining an'extract from each of said earth samples containing any hydrocarbons and organic derivatives thereof which may have been present in said earth samples, transmitting through each of said extracts infrared radiation having wave lengths between 12 and 14 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes the wave lengths between 12 and 14 microns transmitted through each of said extracts.

8. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of desorbing and dissolving any hydrocarbons and organic derivatives thereof contained in said earth from each of said samples, transmitting through each of said extracts infrared radiation having wave lengths between 12 and 14 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes the wave lengths between 12 and 14 microns transmitted through each of said extracts.

9. The method of geochemical exploration for a subterranean petroleum reservoir comprising collecting earth samples froman exploration zone, obtaining an extract from each of said earth samples containing any hydro- 'of contained in said earth samples, weathering each of samples to obtain an extract of wave lengths between somewhat above and somewhat below 12.35:.10 microns and between somewhat above and somewhat below 13.40-* .10 microns, and determining the absorption of the infrared radiation at the wave lengths of 12.35:.10 microns and 13.40i.10 microns as compared with the extent of absorption of the infrared radiation at the wave lengths somewhat above and somewhat below 12.35:.10 microns and somewhat above and somewhat below 13.40:.10 microns.

10. The method of geochemical exploration for a subterranean petroleum reservoir. comprising collecting earth samples from an exploration zone, extracting each of said earth samples with a solvent capable of desorbing and dissolving any hydrocarbons and organic derivatives thereof contained in said'earth samples to obtain an extract from each of said samples, transmitting through each of said extracts infrared radiation having a range of] wave lengths between somewhat above and somewhat be-I low 12.35:.10 microns and between somewhat above and somewhat below 13.40:.10 microns, and determining the absorption of the infrared radiation at the wave lengths of 12.35 :10 microns and 13.40:.10 microns as compared with the extent of absorption at wave lengths somewhat above and somewhat below 12.35 :.10 microns and somewhat above and somewhat below 13.40:.10

microns.

11. The method of identifying an earth sample constituent as having an origin in petroleum comprising transmitting through said constituent infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.351210 microns and over a range of wave lengths which includes at least the wave length of 13.40:.10 microns transmitted through said constituent.

12. The method for identifying a constituent in an earth sample as having an origin in petroleum comprising obtaining an extract from said earth sample containing any hydrocarbons and organic derivatives thereof which may have been present in said earth samples, transmitting through said extract infrared radiation having a range of wave lengths which includes the wave lengths of 12.35:.10 microns and 13.40:.10 microns, and determining the extent of absorption of the infrared radiation over a range of wave lengths which includes at least the wave length of 12.35 i.10 microns and over a range of wave lengths which includes at least the wave length 'of 13.401210 microns transmitted through said extract.

Dooley June 15, 1943 Stevens Mar. 14, 1950 

1. THE METHOD OF GEOCHEMICAL EXPLORATION FOR A SUBTERRANEAN PETROLEUM RESERVOIR COMPRISING COLLECTING EARTH SAMPLES FROM AN EXPLORATION ZONE, OBTAINING AN EXTRACT FROM EACH OF SAID EARTH SAMPLES CONTAINING ANY HYDROCARBONS AND ORGANIC DERIVATIVES THEREOF WHICH MAY HAVE BEEN PRESENT IN SAID EARTH SAMPLES, TRANSMITTING THROUGH EACH OF SAID EXTRACTS INFRARED RADIATION HAVING A RANGE OF WAVE LENGTHS WHICH INCLUDES THE WAVE LENGTHS OF 12.35$.10 MICRONS AND 13.40$.10 MICRONS, AND DETERMINING THE EXTENT OF ABSORPTION OF THE INFRARED RADIATION OVER A RANGE OF WAVE LENGTHS WHICH INCLUDES AT LEAST THE WAVE LENGTH OF 12.35$.10 MICRONS AND OVER A RANGE OF WAVE LENGTHS WHICH INCLUDES AT LEAST THE WAVE LENGTH OF 13.40$.10 MICRONS TRANSMITTED THROUGH EACH OF SAID EXTRACTS. 